Bump from the dead. Might be common knowledge but...
2002/2003 WRX Sedan Front and Back seats will fit in a 95-99 Legacy Sedan.
A couple of notes though: You have to use your Legacy seat belt clip and a spare nut/bolt. The lowest position of the WRX seat is only slightly lower than the highest position of the Legacy seat. Only 4 of 5 front seat bolts line up. The rear seats fit well although there is a slight gap so you can see the top of the strut from the rear triangle window. Despite this, it's worth it, the stock Legacy seats are crap!
Now, which year WRX Wagon seats will fit a 2004 Impreza wagon? I assume: 2002-2007 Front will fit, 2002-2005 Rear will fit? Anything else?